1. Field of the Invention
A method and an apparatus for characterizing contaminants of interest in a fluid flow system like a pipe, duct, or channel using interactive tracers. Various types of interactive tracers may be used, including reactive and partitioning tracer gases and liquids. The method works on fluid flow systems using gaseous tracers in which the liquid contents have been removed or are partially removed. The method will also work for fluid flow systems that filled or partially filled with a liquid. The tracers are selected to detect, locate, and measure the concentration of specific contaminants of interest. These contaminants may accumulate as a liquid, film, residue, or particulate build-up on the walls of the system, in low elevation points, or at appurtenances and geometric constrictions or flow constrictions. This method has application for characterizing contamination in pipe and ducts that once contained chlorinated solvents, petroleum products, radioactive materials, heavy metals or other types of hazardous substances and hazardous waste. This invention has immediate application for decontamination and deactivation (D&D) activities at the U.S. Department of Energy's (DOE's) nuclear sites, such as the Hanford Site, and various industrial and petroleum facilities. This invention also determines when the decontamination operations have been successfully completed.
2. Brief Description of Prior Art
Within the U.S. Department of Energy (DOE) inventory, there are several thousand miles of piping and ductwork from facilities throughout the United States that are ready for deactivation and decommissioning (D&D). A similar problem exists in industrial and chemical/petroleum facilities that are taken out of service for closure or for maintenance and cleaning. These piping systems have been used to move various types of contaminated fluids (liquids and gases) from one area to another within a facility. The ductwork moved air within the facilities through ventilation systems. Over the course of the operation of these facilities, these passageways have become contaminated with the residual hazardous and radioactive materials that they transported. Chlorinated solvents such as trichlorethylene (TCE) and carbon tetrachloride (CCl4) which were used as degreasers at many industrial complexes both within the DOE and the Department of Defense (DOD) facilities, are an examples. Many of the piping systems or large sections of piping are inaccessible and external inspection techniques that require access to the outside wall of the pipe cannot be used. Many of the pipes are buried underground, or are located beneath the floor of a building or beneath paved areas. Because direct access to the external pipe wall is not frequently possible, methods that involve internal inspection of the pipe need to be used. These methods generally require that any liquid in the pipe be removed before the inspection method can be applied.
A common measurement approach for determining whether or not a pipe of duct is contaminated is to use a camera to inspect the inside of the pipe. For short sections of pipe, a small camera is inserted into the pipe on a cable. For example, in U.S. Pat. No. 6,359,645, Sivacoe describes a method of inspecting a pipe, by pushing a video camera through the pipe on a cable. In U.S. Pat. No. 5,939,679, Olsson describes an electromechanical system for inspecting the inside of pipes over distances of several hundred feet for defects and obstructions using a push-cable that mechanically and electrically connects a video camera head to a push reel and video circuit. In addition to cable-inspection systems, a “pig” can be inserted into the pipe to inspect the pipe wall for integrity over the entire length of the pipe. In U.S. Pat. No. 6,243,657, Tuck, et. al., describes a pipe wall inspection system using a pig having an inertial measurement unit and a magnetic sensing system for finding wall anomalies.
A camera and other pipe inspection sensors can be mounted on a robotic vehicle, which is inserted into the pipe and allowed to move down the pipe. For example, in U.S. Pat. No. 6,427,602, Hovis, et. al., describes a crawler for inspection of the integrity of 3- to 4-in. diameter piping, where the crawler can carry sensors or a camera to perform the inspection. This approach is acceptable for larger diameter piping, but for small piping, the robotic vehicle may be too large to be used or not be able to move past bends and constrictions in the pipe. The robotic vehicle can be instrumented with a camera, chemical sensors, and sample collectors. Where access to the pipe is possible, the pipe is sometimes cut and analyzed for contamination in the laboratory.
In general, most methods of finding contamination require the insertion of a physical device into the pipe such as a cable, crawler, or pig. There are many nondestructive pipe inspection techniques, some of which are added to these physical delivery systems, and some of which propagate down the pipe. Most of these methods and apparatuses involve the use of nondestructive testing techniques such as eddy current, ultrasonic, and magnetic flux sensing technologies and all of these technologies involve assessing the integrity of the wall of the pipe, not finding contamination in the pipe.
As DOE begins decontaminating and decommissioning of their facilities, innovative methods to determine the type and level of contamination that is present in the pipe and ductwork are needed for cost-effective and safe D&D operations. DOE has been seeking methods that improve the cost, efficiency, effectiveness and safety of these activities. Non-invasive or minimally invasive methods are sought.
The method of the present invention uses tracers to characterize the contamination in the pipe, where at least one of the tracers does not interact with the contaminant of interest in the pipe, and one or more tracer do. Tracers have been used for characterizing subsurface contamination between monitoring wells such as Dense Non-Aqueous Phase Liquids (DNAPLs), Non-Aqueous Phase Liquids (NAPLs), and Light Non-Aqueous Phase Liquids (LNAPL's) such as unleaded gasoline and diesel. Such methods have been used in both the saturated zone using the natural groundwater flow at the tracer carrier fluid or in the vadose zone using an established air flow field as the tracer carrier. In U.S. Pat. No. 6,321,595, Pope, et. al., teaches a method of characterization of organic contaminants in subsurface formations such as nonaqueous phase liquids by injecting partitioning and non-partitioning tracers at one well point and measuring the arrival times of these tracers at another well point. This subsurface tracer approach has also been used to detect releases of a hazardous liquids from underground and aboveground storage tanks. While none of these approaches have been used to identify the presence of contamination inside a pipe or a duct, these methods have identified a variety of partitioning tracers that can be used in the method of the present invention for characterizing contamination in fluid flow systems such as pipe and ducts, which in many instances is the source of the subsurface contamination.
Various tracer methods have also been used for detecting and locating a hole in a tank or a pipe, but none of these methods are used to find contamination in the tank or pipe.
There are a number of important advantages of the method of the present invention over the physical delivery systems currently used for characterizing contamination in pipe and ductwork. The first advantage of the proposed invention is that the same procedure will work on pipes (or ducts) of any size and nearly any length. Tracers are just as easily injected into a small diameter pipe (e.g., 0.5 in.) as they are into larger diameter pipe (e.g., 12 in.). Other remote pipe inspection equipment, which transport cameras by crawlers into a pipe, require pipe diameters of 4 in. or larger for entry and operation. Many of the pipelines within building systems are on the order of 0.5 to 2.0 inches, making inspection using cameras nearly impossible.
The second advantage of the proposed invention is that the injected tracers can easily navigate pipe (or duct) bends and other pipe irregularities with ease compared to remotely operated inspection equipment. Tight bends and changes in diameter are not a problem for the tracer gases, yet represent major hurdles for other characterization techniques. Gas tracers also inspect the entire surface of the pipe, including any crevices or nooks that may be difficult to inspect using video approaches. This will result in a more complete and thorough inspection of the pipe (or duct).
The third advantage of the proposed invention is that there are no moving parts or equipment that has to enter the pipe. For pipes or ducts that may contain explosive vapors or contaminants that could ignite, the partitioning tracer technique offers a characterization approach that remains safe. In addition, since no mechanical equipment enters the pipe, this eliminates the possibility of equipment malfunction or getting “stuck” and “plugging” the pipe (or duct).
The fourth advantage is that equipment contamination and de-contamination is avoided. This has both safety and cost implications. Because no equipment enters the pipe, there is no equipment that must be decontaminated when it exits the pipes. This reduces the amount of investigation-derived wastes that need to be disposed of properly.
The fifth advantage of the proposed invention is that it can be operated more cost effectively and more safely than other techniques without sacrificing performance. In fact, the performance of the proposed invention should be better than the more conventional methods.
In addition to being a very advantageous approach for the end users, the proposed invention can also be used in a variety of detection and measurement scenarios. The most common scenario is to characterize a pipeline or duct system to determine if the pipeline has any residual contamination that must be removed before the pipe or duct can be decommissioned or released. The proposed invention can also be used before and after a decontamination event to validate the amount of contamination that has been removed from the pipeline by a particular decontamination technology. Finally, the proposed invention can also be used to routinely monitor pipelines and ductwork to monitor any residual buildup of contaminants that could reduce efficiency of the pipeline.
The method described is motivated by the D&D need. As a consequence, it is described in terms of gaseous tracers, because in most D&D activities, all of the liquid contents of the pipe are removed before any attempt to clean the pipe is done. Cleaning is typically done by flushing the pipe with water or some other cleaning chemical. The liquid used to flush the pipe is removed before any attempt to determine if any residual contamination exists. With properly selected interactive tracers, the method of the present invention can be applied using either gaseous or liquid tracers.